Keeping communication private has become increasing important in an era of mass surveillance and cyberattacks. For example, government officials and business leaders travel to hostile locations and risk revealing confidential information when they rely on local, untrusted infrastructure to communicate using mobile devices and computers. Additionally, even in friendly locations, servers and internet service providers may be untrusted. Many people are also concerned that communication is being monitored by private parties and government agencies. Not only are people concerned with content of communication being discovered, but metadata surrounding the communication as well. Metadata may contain information about the communication including identities of parties that sent and received the communication, a time of the communication, and a frequency of the communication. Although communication may be encrypted to protect content of the communication, maintaining privacy of associated metadata is an increasingly important challenge.